1. Field of the Invention
The present invention pertains to stackable riser sections and riser covers for creating access risers. More particularly, the present invention pertains to the structural elements of a riser section for connecting a series of riser sections to each other, and to an upper cover.
2. Discussion
Stackable risers are used to provide access to underground containments or vessels made of concrete, typically associated with septic systems, and/or underground electrical or communications systems. Riser sections are disclosed in U.S. Pat. Nos. 6,484,451 and 6,655,093. The latter patent also discloses a riser cover. The content of these patents is hereby incorporated by reference into this specification.
Injection molded, plastic, stackable riser sections made of high density polyethylene and other rigid, light weight polymeric material are known in the art and provide access to underground vessels. Riser sections can be manufactured in various heights and diameters, and a series of identically sized riser sections can be stacked to achieve a desired depth. A removable cover is provided on the top riser of a stack to permit access to the underground vessel.
Depending on the soil characteristics and overhead traffic, the vertical, horizontal, and rotational forces placed upon these riser sections can be considerable. It is important to continually evolve the riser structure design to maximize the resistance of the riser and cover stack to these loads.
The riser section and riser cover disclosed for example in U.S. Pat. No. 6,655,093 represent a satisfactory system for providing access to underground vessels. Evolution of these products has resulted in riser section and cover combinations which display superior load carrying capabilities and which can be reliably manufactured by the same molding processes as have been previously used. The present invention is directed to such combinations.
The stackable riser sections of the present invention have a hollow, cylindrical sidewall configuration, although configurations other than cylindrical may be used. The sidewall of the riser section includes a channel end and a blunt end which interengage or nest with adjacent riser sections to form a vertical stack.
The blunt end of the riser section sidewall, usually the upper end, terminates in a blunt, or square, end that defines a flat annular edge surface. The blunt end of the riser section sidewall is configured to mate with the channel end of either another riser section or a cover.
The opposite, channel, end of the riser section, usually the bottom, includes two adjoining channels defined by interior, slotted middle, and truncated exterior wall portions that extend down from a horizontal ledge portion extending inwardly from the sidewall. The wall portions of the channel end project concentrically with, or (in the case of riser sections having, for example, a square or rectangular cross-section) parallel to, the sidewall.
The radially outer channel is defined between the slotted middle wall and the truncated exterior wall. The truncated exterior wall defines a downwardly facing flat annular edge surface adopted to be disposed in closely spaced facing relation to the flat annular edge surface of the blunt end of an adjacent riser when stacked together.
The outer channel is shallower than the inner channel and is, in essence, a seal groove. It accepts a resilient seal element. The seal element is compressed against the flat annular edge surface of the blunt end of an adjacent riser to effect a water-tight and gas-tight seal between two stacked riser sections (or between a riser section and a cover).
A plurality of spaced, vertical support bosses are connected to the interior surface of the cylindrical sidewall of the riser by webs that are narrow relative to the circumferential width of the bosses. The bosses extend from the horizontal ledge portion at or near the channel end to the flat annular edge surface at the blunt end of the riser section sidewall. The bosses strengthen the sidewall and provide vertical support for an adjacent upper riser section.
The radially inner channel is substantially larger than the outer channel, and accepts the interior vertical support bosses of a riser section on which it rests. Portions of the slots of the middle wall of the channel end are defined by parallel side edges spaced apart a distance narrower than the bosses but wider than the webs. The slots receive the webs that connect the bosses to the sidewall to permit positioning of the bosses within the inner channel of an adjacent riser section positioned above it with the portions of the slotted wall defining parallel edges positioned between the bosses and sidewall of the lower riser section. At the interconnection between each pair of stacked riser sections the webs of the bosses interengage with the slots of the slotted middle wall of the associated stacked riser. Radial or horizontal loads are received by the slotted middle wall at the portions defining the parallel slot defining edges.
The inner wall portion is an annular member with significant hoop strength. Loads imparted to the middle wall portion by the bosses are shared with the inner wall through the connecting ledge portion.
The bosses are displaced radially inward of the slotted middle wall and capture the middle wall of a stacked riser section between the inner surface of the riser side wall and the radial outer surface of the bosses. The slotted middle wall includes thickened wedge portions which frictionally engage the bosses when one riser section is fully nested on another riser section. This ensures a snug fit. The cover is arranged to provide this same fit with a top riser section.
Projections on the bottom of the horizontal ledge portion in the inner channel are aligned with the slots and support the upper riser section on the bosses of the lower riser section. The projections transfer downward forces from above to the top ends of the bosses located below the projections.
A cover is adapted to be secured to the top of the uppermost riser section. Like the stackable riser, the preferred shape is cylindrical, but other configurations, such as square, rectangular or elliptical may be used with correspondingly shaped riser sections.
The cover has a top surface and a bottom surface, with the top surface being nearly smooth and slightly convex. A sidewall of the cover depends from the top surface. It includes a channel end similar to the channel end of the riser sections. The channel end includes two adjacent concentric channels defined by inner, slotted middle and outer truncated wall portions. The truncated outer wall defines the sidewall outer surface of the cover and terminates in a downwardly facing flat annular edge surface similar to the flat annular edge surface on the upper blunt end of the riser sidewall. A seal is located in the outer channel and is compressed by the flat annular edge surface of the lower riser when the cover and riser sections are nested together.
The cover inner channel is defined between the inner wall and the slotted middle wall. It receives the bosses of the riser section below the cover. Projections similar to the projections in the inner channel of a riser section are provided in the inner channel of the cover. They are aligned with the slots of the middle wall. The projections contact the upper end of the bosses of the riser section below the cover and transfer vertical loads imparted to the cover to the bosses below the projections. The inner channel also includes spaced radial webs extending between the middle wall and the inner wall adjacent each slot. These webs transfer load between these walls.
Each boss may be adapted to receive a screw, or other fastener, that extends through the horizontal ledge portion of a riser section stacked above the blunt end for securing the upper riser section to the lower riser section. The bosses also may receive a screw to attach a cover at the top of a riser stack.
Other features, objects and advantages of the invention will become apparent from the following description and drawings in which the details of the invention are fully and completely disclosed as part of this specification.